This invention relates to absorbent products and particularly to such products provided for absorbing body fluids, as for example, catamenial napkins, tampons, diapers, wound dressings and the like. Specifically, this invention relates to employing, as an absorbent media in such products, cellulose fibers which have been crosslinked with a specific class of crosslinking agents and which have the properties of high absorbency and retention of body fluids.
Cellulose has long been used as an absorbent material for absorbing body fluids in that it is a cheap, abundant and relatively absorbent material. This notwithstanding, the art has searched for improvements in the absorptivity of cellulose in an effort to reduce the bulk of absorbent products or to reduce their cost and several suggestions have already been made proposing that cellulose be chemically modified to achieve these goals.
One such proposal is found in U.S. Pat. No. 3,241,553 issued to Fred H. Steiger on Mar. 22, 1966 wherein it is disclosed that the absorption and retention capacity of absorbent products utilizing cellulosic fibers may be increased by first crosslinking the fibers. As is described in this patent, the crosslinking greatly increases the resiliency of a body of fibers in the wet state thereby increasing the interstitial volume between fibers and hence, the volume of fluid which can be held therein. The crosslinking, however, does not increase the quantity of fluid held within a fiber, this being dependent on the basic hydrophilicity of the starting cellulosic itself. Thus, from the teaching of this reference, crosslinking will increase the absorbency of both hydrophilic and relatively hydrophobic cellulosics. This teaching has been applied in U.S. Pat. No. 3,589,364 issued to Walter Lee Dean, et al. on June 29, 1971. Disclosed therein is highly absorbent cellulosic fibers comprising the product of two chemical reactions, to wit: the carboxymethylation of cellulose wherein hydroxyl groups on the anhydroglucose units in the cellulose chain are carboxymethylated to a high degree of substitution and the crosslinking of the cellulosic chains. Produced is an insoluble, fibrous mass which, by virtue of the crosslinking, maintains its fibrous integrity and hence, has a high interstitial volume and a high interfiber capacity for fluids and which, by virtue of the inherent hydrophilicity of carboxymethylated cellulose, has a high intrafiber absorption capacity.
Unfortunately, while the aforementioned hydrophilic crosslinked fibers represent a great improvement over unmodified cellulose, complex processing is required to obtain these properties. Basically, two separate chemical reactions must be carried out, the carboxymethylation and the crosslinking. Thus, two reagents are involved and the product of reactions must be washed free of both of these reagents. In view of the complexity of the process required to produce such an absorbent fiber, the ultimate cost to the consumer of products incorporating such fibers is high and much of the advantages in substituting such fibers for unmodified cellulose is lost.